The present invention relates to heavy vehicle ABS modulators that presently use flow-through solenoids with complex pilot passages. In the field relating to antilock braking systems "ABS," a modulator valve is situated between a source of air pressure and the brake chamber or actuator. The modulator is typically a three-way valve that under normal service operation selectively receives pressurized air upon depression of a brake valve and conveys the pressurized air to the brake actuators. Likewise, release of the brake valve shuts off the supply of air pressure to the brake actuators.
If an antilock event is sensed, an electronic control unit sends suitable signals to a solenoid valve assembly (usually a pair of solenoid valves) associated with the modulator. The solenoid valves provide an electro-pneumatic interface between the electronic controller and the air brake system. If an impending wheel lockup is sensed, the antilock controller immediately begins to modify brake application using the modulator. The coils associated with the respective solenoid valves are energized or de-energized in a predetermined sequence by the controller. As is known in the art, when a solenoid coil is energized, a core or shuttle is moved to either open or close an associated air passage. This either opens or closes the exhaust passage or reapplies air pressure to the brake actuator. Each of the solenoid valves is independently controlled by the electronic control unit. By opening and closing the solenoid valves, the antilock controller simulates brake "pumping" but at a rate substantially faster than the driver of a vehicle could actually pump the brakes to avoid skidding.
Although systems of this general type have met with substantial commercial success, there is always a need for improved efficiency and reduced manufacturing complexity. Associated with known arrangements is a relatively complex series of flow passages that interconnect the supply solenoid valve, exhaust solenoid valve, supply diaphragm, exhaust diaphragm, the supply or inlet port, the exhaust port, and the delivery port. Included among these complex flow passages are a series of pilot passages that interconnect the various components of the valve, i.e., pilot passages lead from opposite ends of the pair of solenoids to one of the diaphragm valves or to an exhaust passage.
Selected ones of these passages are used for connecting the flow passages to the exhaust port. The longer these passages are, the slower the reacting time in releasing the brakes. For example, when the foot or brake valve is released, it is preferred that the modulator be quickly and effectively connected to exhaust so that the brake actuators are released.
Moreover, known designs use flow-through solenoid valves which, although effective, require seals at each end and O-rings along the length thereof.
Thus, it would be desirable to provide a non flow-through solenoid valve assembly for heavy vehicle ABS modulators that overcome the noted problems.